Conventionally-used golf club shafts are generally made of steel, metal alloys, or composite materials. They possess a slightly conical shape and continuous variation of their section, whose maximum dimension is measured at the grip, or handle, and the minimum dimension, at the neck, where the head of the club is attached. This remains the most widely-used shaft geometry.
If one wishes to vary the mechanical properties of the shaft, i.e., in particular, the moment of inertia and the elastic line under torsion and flection, the opportunities for such changes on these shafts are rather limited. The addition of inertia blocks or reinforcements at different places on the shaft is not a satisfactory solution, since one part of the club is made heavier, a generally undesirable effect. One example of an embodiment of this kind is given in Patent No. JP 1-159 879, which describes the fabrication of a shaft made of composite materials comprising reinforcement zones produced by adding pieces formed from layers of resin-impregnated fiber sheets to the body of the shaft. A second disadvantage of this construction arises from the lack of continuity of the fiber sheets at these reinforcement sites, thereby appreciably impairing the reproducibility of the mechanical properties from one shaft to another and thus limiting their use by professionals.
Similarly, Patent No. GB 256,049 describes a golf club fitted with a metal shaft on which flexible areas of contraction are produced so as to modify the curve of deformation under flection and thus, to improve the elastic response of the club. While flection properties are, in this case, controlled and optimized, the torsion properties, in particular, are poorly controlled, mainly because of the homogeneous, non-fibrous nature of the material used.